                U.S. Pat. No. 4,966,459 discloses a method of detecting broadband ultrasound from materials using a confocal Fabry-Perot interferometer.        U.S. Pat. No. 6,041,020 discloses a method of detecting ultrasound using a cw laser to sense airborne ultrasound radiated from materials.        U.S. Pat. No. 6,484,052 discloses a method where pulsed laser-generated ultrasound is used to enhance the delivery of therapeutic compounds.        U.S. Pat. No. 6,668,654 discloses a method of dividing the laser pulse into spikes such that the generated ultrasound has a particular shape.        U.S. Pat. No. 6,833,554 discloses a method for pulsed generation and optically detecting shear waves in materials.        U.S. Pat. No. 6,809,991 discloses a method that selects an excitation signal, transmits, and detects the signal in an opaque solid, as in the detection of land mines.        U.S. Pat. No. 7,117,134 discloses a method to optimize the laser generation of ultrasound to improve the accuracy of the testing.        U.S. Pat. No. 7,278,315 discloses a laser-ultrasonic method to detect subsurface defects in using Rayleigh waves.        U.S. Pat. No. 7,474,411 discloses a method to optimize the laser generation of ultrasound to improve the accuracy of the testing.        U.S. Pat. No. 7,516,662 discloses a method where railway tracks are inspected using pulsed laser generation of ultrasound in the rails and detected by a cw laser with an optical interferometer        U.S. Published Application 2004/0003662 discloses a similar method to U.S. Pat. No. 7,516,662 except that detection is performed with an air-coupled transducer.        